The present invention relates to a wiring material of semiconductor devices. Specifically the present invention relates to a semiconductor device having a circuit comprising a thin film transistor (hereinafter referred to as TFT), and a manufacturing method thereof. For example, the present invention relates to an electro-optical device, which is represented by a liquid crystal display panel, and an electronic device with an electro-optical device loaded as a component.
In this specification, a semiconductor device indicates general devices that can function by using semiconductor characteristics, and that electro-optical devices, semiconductor circuits, and electronic devices are all categorized as semiconductor devices.
Recently, techniques for using semiconductor thin films (with a thickness of about several nm to several hundreds of nm) formed over a substrate having an insulating surface to constitute a thin film transistor (TFT) have been in the spotlight. Thin film transistors are widely applied to electronic devices such as ICs and electro-optical devices, and the development thereof as switching elements for image display devices is hastened.
Conventionally, aluminum films formed by sputtering and having low resistivity have been often used as the wiring material for the above stated TFTs. However, when a TFT is manufactured by using aluminum as a wiring material, operation error or deterioration of TFT characteristics were caused by formation of projections such as hillocks or whiskers or by diffusion of aluminum atoms into the channel forming region, in the heat treatment.
As stated above, aluminum is not a preferable wiring material in the TFT manufacturing process because of its low heat resistance.
Therefore, materials comprising, for example, tantalum (Ta) or titanium (Ti) as a main component are being tested for use as a wiring material other than aluminum. Tantalum and titanium have a high heat resistance in comparison to aluminum, but on the other hand there arises a problem of high electrical resistivity. Further, if tantalum is performed with heat treatment at a temperature of about 500 C, it becomes a problem that the electrical resistance increases by several times in comparison with that before heat treatment.
Furthermore, in the case that a film formed on a substrate possesses a large stress, substrate warping and film peeling generate, so it is preferable to perform film stress control and to form a film which possesses as low a stress as possible for a film formed by sputtering. As one means of controlling film stress, the use of a mixed gas of argon (Ar), krypton (Kr), xenon (Xe) as a sputtering gas has been proposed. However, since krypton (Kr) and xenon (Xe) are expensive, it is unsuitable for cases of mass production to use the mixed gas.